1. Field of the Invention
The present invention relates to interconnect systems for connecting multiple inkjet pens in an inkjet printer. More specifically, the present invention relates to flexible interconnection circuits used for connecting multiple inkjet pens in an inkjet printer.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
Inkjet printer/plotters and desktop printers, such as those sold by Hewlett Packard Company, offer substantial improvements in speed over the conventional X-Y plotter. Inkjet printer/plotters typically include a pen having an array of nozzles. The pens are mounted on a carriage which is moved across the page in successive swaths. Each inkjet pen has heater circuits which, when activated, cause ink to be ejected from associated nozzles. As the pen is positioned over a given location, a jet of ink is ejected from the nozzle to create a pixel at a selected location. The mosaic of pixels thus created provides a composite image.
Inkjet technology is now well known in the art. See, for example, U.S. Pat. No. 4,872,027, entitled PRINTER HAVING IDENTIFIABLE INTERCHANGEABLE HEADS, issued Oct. 3, 1989, to W. A. Buskirk et al. and U.S. Pat. No. 4,965,593, entitled PRINT QUALITY OF DOT PRINTERS, issued Oct. 23, 1990, to M. S. Hickman, the teachings of which are incorporated herein by reference.
Recently, full color inkjet printer/plotters and desktop printers have been developed which comprise a plurality of inkjet pens of diverse colors. A typical color inkjet printer/plotter has four inkjet pens, one that stores black ink, and three that store colored inks, e.g., magenta, cyan and yellow. The colors from the three color pens are mixed to obtain various colors.
The pens are typically mounted in stalls within an assembly which is mounted on the carriage of the printer/plotter. The carriage assembly positions the inkjet pens and typically holds the circuitry required for interfacing to the heater driver circuits in the inkjet pens.
A carriage assembly typically consists of four pen stalls to align the inkjet pens, four pen clamps to hold the inkjet pens in the pen stalls, a printed circuit board with circuitry for interfacing the heater circuits in the inkjet pens, and four separate flexible circuits interconnecting the printed circuit board with electrical contacts on the inkjet pens.
The flex circuit is typically made with a polyester or polyamide material such as a Mylar or Kapton substrate onto which multiple conductors or traces are created. A color inkjet printer with four inkjet pens requires four separate flexible circuits. The use of four separate flex circuits has the disadvantages of: 1) high cost due to the need to manufacture and stock the multiple separate flex circuits; 2) difficulty of assembly because of the need to route the flex circuit in the carriage assembly and precisely align each of the flex circuits to each of the pen housings; 3) high cost of assembly because the separate flex circuits need to be separately interconnected with the printed circuit board; and 4) the need to provide separate grounds for each flex circuit. The requirement of separate grounds for each flexible circuit limits the number of ground interconnects available for an inkjet pen. Moreover, separate ground returns for each pen can cause ground fluctuations and a corresponding pen performance degradation if a large number of heater circuits in one inkjet pen are activated simultaneously.
Accordingly, there was a need in the art for an improved interconnect system that reduced cost, was easy to assemble and align, and provided ground plane sharing for all of the inkjet pens. This need was addressed by U. S. patent application entitled AN IMPROVED UNITARY INTERCONNECT SYSTEM FOR AN INKJET PRINTER, filed Apr. 30, 1993 by A. K. Wilson et al., Ser. No. 08/055,615, the teachings of which are incorporated herein by reference. This application discloses and claims an advantageous flexible circuit (flex circuit) for use with inkjet printers. Unfortunately, this flex circuit has a single pattern of contacts and is therefore limited to use with a single contact configuration.
Accordingly, a need remains in the art for a flex circuit for inkjet pens which is not limited to a single pen type.